White smoke out the back end of the truck and the engine just quit - head gasket?

While driving on the freeway I first noticed a pinging noise when accelerating at lower speeds. It became louder and I started to lose power. A I was looking for a safe place to pull over I notice some smoke out the back end of the truck and the engine just quit. After getting a tow I opened the hood to discover the hoses leading to and from the radiator were disconnected. I reconnected them, filled up the system with water and tried to start the engine. It seems to be turning over but will not start. After a minute of cranking I stop and can hear guggling noices and have to put some additional water in. Sometimes the resevoir cap pops off. What could be the problem?